1. Field of the Invention
This invention relates to inorganic paper and a method for its production. More particularly, it is concerned with inorganic paper which is effective as a reinforcing material for composite type plastic sheet, and a method for producing the same.
2. Description of the Prior Art
As the reinforcing materials for the composite type plastics which are in general use, there have so far been known granular inorganic compounds, i.e., fillers, papery base materials with various sorts of pulp being used as the raw material, and, as materials having much higher reinforcing property, various inorganic fibrous compounds represented by glass fibers. These reinforcing materials are used by appropriate selection depending on required performance of the composite type plastics or their manufacturing costs.
The shapes of the composite plastics containing those inorganic compounds as mentioned above take various forms such as, for example, powders, pellets, sheets, and others. However, in the case of manufacturing laminated shaped article, the shape
required is the sheet form. The advantageous feature of the sheet-like shape is such that it can be readily shaped into any configurations as those shaped articles in thick gauge, thin guage, or large size, and those shaped articles in complicated configurations.
As the inorganic reinforcing material in the sheet form, there has so far been known the so-called "unwoven cloth" produced by uniformly dispersing fibrils cut into a length of from a few millimeters to a few centimeters from glass fiber, carbon fiber, etc., or woven cloth of such glass fiber and carbon fiber, and then gluing together the uniformly dispersed fibrils with an adhesive agent. This unwoven cloth is an effective reinforcing material for the composite type plastic. Such reinforcing material is usually required to have resistance against impregnation treatment, because it is subjected, in most cases, to impregnation with liquefied resins or resin liquids using solvents. It is also necessitated to have sufficient binding force to prevent itself from unravelling, when impregnated with the liquefied resin or the resin liquid. Accordingly, the solvent-resistant property, the water-resistant property, and the chemicals-resistant property of the binding agent also constitute important characteristics.
However, such reinforcing material is required to have a continued fiber length or a fiber length of a few millimeters or longer. It is therefore difficult to make those inorganic compounds having very short fiber length such as, for example, whisker or fibrous particles into the woven cloth or the unwoven cloth as mentioned in the foregoing.
When the microfibers such as whisker and fibrous particles are made into continuous sheet such as woven cloth, unwoven cloth, paper, and so forth, a large quantity of binding agent becomes necessary, because no reinforcing effect can be expected from entanglement among the component fibers. Even if such microfiber material is made into a sheet form by use of a large amount of binding agent, the sheet product is disadvantageously brittle and poor in its mechanical strength.